Preparation And Properties Of Nanocellulose Based High Strength And Toughness Hydrogel

Hydrogel is a gel with three-dimensional stereo structure,and the interior of the crosslinked network can swell and maintain a large amount of moisture,which has been widely used in the field of biological tissue,medical beauty,bionic equipment.However,traditional hydrogels have disadvantages of insufficient mechanical strength and low processability,which seriously limit their application and development.Nanocellulose has the characteristics of high modulus,high long diameter ratio,high strength,good biocompatibility and so on,making it an excellent nano reinforcement material.In this paper,nanocellulose（CNF）was prepared by TEMPO-mediated oxidation and introduced into composite multi-network hydrogels as a rigid network.The mechanical properties of composite hydrogels were improved through the enhancement mechanism of CNF and coordination between CNF and multi-network.The main research contents are as follows:（1）Nanocellulose was used as the first rigid network,and polyacrylamine-acrylic acid（PAM-AA）was used as the second flexible monomer network.Fe³⁺was used for double ion crosslinking to obtain composite double network hydrogel.The results show that as the CNF content increases,the mechanical strength of hydrogel also increases.The composite hydrogel tensile strength can reach（6.1±0.5）MPa at 1 wt%CNF,which was approximately 20 times compared to pure PAM-AA hydrogel.The mechanical properties of hydrogel were improved significantly by the double network crosslinking structure.（2）Inspired by bionic muscles cartilage,based on the polyelectrolyte complexing spinning mechanism,designing a set of new spinning system in order to realize the anisotropic layers structure of nanometer fiber cellulose gel preparation,and orderly arrangement to collect it as the first rigid network,through in situ polymerization method（PAM-AA）as a second flexible network.Furthermore,by Fe³⁺crosslinking,a double network hydrogel with double ion crosslinking and high orientation hierarchy structure was obtained.The composite hydrogel has excellent mechanical properties,the elongation at break is up to（838.9±10.2）%,and the tensile strength along the orientation is up to（11.2±0.3）MPa,which was similar to biological tissue.Through the tests of biotoxicity,ionic conductivity and flexible sensing,the hydrogel showed excellent biocompatibility and ionic conductivity.When the content of lithium chloride was 1.5 wt%,the ionic conductivity of the hydrogel reached 0.022 S/cm.（3）In order to improve the toughness of hydrogels,polyvinyl alcohol（PVA）third network was introduced into PAM-AA/CNF hydrogels with random orientation,and semi-crystalline structure triple network hydrogels were prepared by freeze-thaw treatment.The prepared triple-network hydrogels were prestretched,Fe³⁺was crosslinked and fixed with different pre-stretched strains to obtain high-orientation triple-network hydrogels.Due to the hydrogen bond and physical entanglement between PVA and PAM and PAA,as well as the self-crosslinking of the semi-crystalline microregion of PVA,the elongation at break of the composite triple network hydrogel can reach（1280.5±13.4）%.When the pre-tensile strain was 700%,the tensile strength of hydrogel is（9.5±0.4）MPa,and the mechanical properties of hydrogel gradually improve with the increase of CNF content.When the content of lithium chloride was 1.5 wt%,the ionic conductivity of hydrogel is 0.03 S/cm,showing good ionic conductivity.